1. Field of the Invention
The present invention relates to a wireless communication device preferably for use in a radio-frequency identification (RFID) system and a short-range wireless communication system.
2. Description of the Related Art
A planar coil antenna is generally used in a high frequency (HF)-band RFID system that uses near field communication (NFC), and is mounted on a mobile terminal such as a cellular phone terminal or a mobile information terminal.
On the other hand, a reduction in thickness of the wireless communication device such as the cellular phone terminal has been accelerated recently and the case where a metal housing is used (including the case where metal plating processing is performed on a resin housing) has been increased in order to cope with insufficient strength due to the reduction in thickness or attempts to improve design properties.
When metal is used for the housing, however, the planar coil antenna that is incorporated in the terminal opposes a metal surface and an induction current (eddy current) cancelling a signal current of the planar coil therefore flows through the metal surface. Due to this, the planar coil antenna is shielded by the metal surface and cannot communicate with a device of another party.
On the other hand, for example, International Publication No. 2013/069465 discloses an antenna device in which a planar coil antenna is arranged so as to be close to a metal member. The antenna device in International Publication No. 2013/069465 enables an NFC antenna to be used even in the device in which the planar coil antenna is arranged so as to be close to the metal member by providing an opening on the metal member causing at least a part of the planar coil antenna to be exposed.
In the antenna device as disclosed in International Publication No. 2013/069465, the opening is formed on the metal member so as to have an opening area that is substantially the same as that of a coil pattern of the planar coil antenna. Therefore, when the metal member is used for the housing, the mechanical strength of the housing itself lowers. In particular, in a device having a large area and being reduced in thickness, such as a mobile terminal or a tablet PC, lowering of the mechanical strength of the metal housing needs to be avoided. Further, when the opening is exposed to the outer surface, the design of the outer appearance is largely constrained. Further, when the above-mentioned metal member is used as an electrostatic shield member, an electrostatic shield effect lowers in the opening and there arises a problem in electric characteristics.